BIRDS OF NEW YORK 67 



more and more difficult to add a new bird to the list. The observer must 

 be ubi(iuitous in mio;ration time. 



The time of arrival is several days earlier in the southern part of the 

 the State and in the lower altitudes than it is in the Adirondack district 

 and the Alleghany plateau. The variation in the time of arrival, both at 

 different stations in the State, and in different years at the same station, 

 is greatest in the case of those birds which arrive during February, March 

 and early April, the difference being sometimes three or four weeks. Birds 

 like the Bobolink and Baltimore oriole, which come early in May, arrive 

 at nearly the same date in all jxirts of the State [see map, ]>. 66], and 

 their time of appearance varies only a few days at each station. Sometimes 

 an unusuall\- wiu-m wave, early in the season, will liring bluebirds and 

 redwings on the same date to nearlv everv station in the mi<ldle districts. 

 This was the case on the 24th of February 1906, when these birds appeared 

 in considerable numbers at Ithaca, Canandaigua, Rochester and other 

 ])laces. These facts seem to indicate that our l)irds can travel the whole 

 width of the State in a single da\' during the migration if weather condi- 

 tions are favorable, but a studv of the tables following page 74 will show- 

 that the average date of arrival is several days later for the more nortliern 

 and the more elevated districts. 



There can be no doubt that the arrival of birds with vis depends upon 

 the temperature and probably u])on the winds. With the advance of a 

 low cvclonic center from the southwest, bringing high temperature to 

 western New York in March, Aj^ril or May, there is sure to be a bird wave 

 which corres] )( )nds in magnitvide to the wami weather wave which undoubted- 

 ly brought it. Manv facts seem to show that the birds of western and north- 

 ern New York are mostly immigrants from the southwest, and the wami 

 wc>ather as well as the ]n-e\'aihng winds of this region also come from that 

 direction. The warm weather at least furnishes the favorable conditions 

 which induce them to migrate. These are no more an agreeable temperature 

 than an abundance of food and favoring winds to aid their ardvious ])assage- 



